The present invention relates to a two-cycle engine with a direct fuel injection system, and more particularly to a fuel injection control system with a two-stream injector.
In a two-cycle engine where fuel is mixed with air to make a combustible mixture and the mixture is supplied to a cylinder of the engine, a part of the fuel escapes from the cylinder through an exhaust port at the scavenging of the cylinder. A method is proposed to prevent fuel from escaping through the exhaust port, where air alone is delivered to the cylinder and fuel is injected directly to the cylinder by an injector. However, since the fuel injection occurs during the compression stroke, the fuel must be injected at a high pressure. Accordingly, there has been proposed a fuel injection system where fuel is injected by a two-stream injector with compressed assist air.
Japanese Patent Laid-Open 62-93481 discloses an injection control system in which a measured amount of fuel is accumulated in the injector before the fuel injection, and then the accumulated fuel is injected by compressed air at the opening of an injection valve. Additional fuel is further injected during the air injection. The irregular fuel injection is intended to charge stratification near layers around the spark plug. An experimental laser beam measurement of gas flow in the cylinder in the conventional system showed that gas flow largely fluctuates in each cycle. Accordingly, the stratified charge is moved at every cycle, so that uniform combustion does not occur.
Further, a larger amount of fuel is injected at the first injection compared with the second injection. Consequently, the injected fuel is not uniformaly mixed with air. In addition, residual gases remain in the cylinder and the fuel is injected in the mixture of fresh air and the residual gases. Consequently, the amount of the fresh air is small, which makes it difficult to ensure the stable ignition of the fuel.